It is shown that the low-energy $\overline{K}N$ scattering data imply a large breaking of $\mathrm{SU}\left(3\right)\mathrm{}$ symmetry in the ${Y_0}^{*}\mathrm{}\left(1405\right)\mathrm{}$ couplings. The coupling of this resonance state to the $\overline{K}N$ system is found to be several times larger than what is expected on the basis of assigning it to a ${\mathrm{½}}^{-}$ $\mathrm{SU}\left(3\right)\mathrm{}$ singlet and using its decay width into $\pi \Sigma$. Two theoretical calculations are carried out in order to understand this breaking effect. The first calculation uses a vector-exchange-potential model; the second, algebras of currents. The calculations succeed in relating the symmetry breaking to mass differences. The ${\mathrm{½}}^{-}$ singlet $\mathrm{SU}\left(3\right)\mathrm{}$ assignment for the resonance retains its validity.

• Received 12 May 1967

DOI:https://doi.org/10.1103/PhysRev.161.1682